In optical information communication, optical fibers which serve as transmission media have been required to have larger transmission capacity as communications traffic increases. Particularly, a long-distance transmission optical fiber employing Wavelength Division Multiplexing (WDM) has been keenly required to meet such requirement. Further, it is predicted that the communications traffic will continue to increase. Therefore, increase in the transmission capacity of the optical fibers is an urgent object to be attained.
In order to increase transmission capacity of an optical fiber, it is necessary to increase power of signal light to be supplied to the optical fiber. However, increase in the power of the signal light to be supplied to the optical fiber increases power density in a core, thereby causing problems such as production of a nonlinear optical effect and generation of fiber fuse. It is therefore necessary to increase an effective core area of the optical fiber so as to (i) avoid the problems and (ii) increase the transmission capacity of the optical fiber by increasing the power of the signal light to be supplied to the optical fiber.
The optical fiber whose effective core area is increased is exemplified in Patent Literatures 1 and 2.
Patent Literature 1 describes a technique of increasing, to 120 μm2 or more, an effective core area of a single-mode fiber having a depressed refractive index distribution. Patent Literature 2 describes a technique of increasing, to 130 μm2 or more, an effective core area of an optical fiber which has a core including a first core layer (high refractive index), a second core layer (low refractive index), and a third core layer (intermediate refractive index). The single-mode fibers described in Patent Literatures 1 and 2 have no mode dispersion and, also in this respect, have an advantage in having larger transmission capacity.